Ceramic Shell Investment Casting

Ceramic Shell Investment Casting

The ceramic shell investment casting process is used to make metal parts that are difficult to shape through other methods.ceramic shell investment casting The process begins with a wax pattern that closely resembles the desired casting. This is assembled in a tree structure along with sprue poles and runners to create a "lost wax" cast. The wax patterns are dipped in ceramic slurry mixtures and coated with a refractory material, such as sand or stucco. As the coatings dry, they become a ceramic shell that enables the molten metal to be cast inside of it. Unfortunately, the ceramic shells are prone to cracking and breaking when exposed to high temperatures.

The refractory used in the ceramic shells is often made from a combination of materials, including alumina and silica.ceramic shell investment casting The choice of refractory material is based on such factors as mould drying effectiveness, slurry characteristics and mechanical strength. The slurry composition is also selected to achieve the required refractoriness and mechanical strength, while providing adequate permeability for moulding.

In the current practice of ceramic shell production, it is important to ensure that the ceramic slurry has an adequate amount of face-coat and back-up materials. This will ensure that the ceramic shells are able to withstand the high temperature exposure throughout the casting and firing stages, while maintaining sufficient permeability. Additionally, the ceramic shells must possess sufficient strength to withstand knock-out and deformation during the casting and dewaxing processes.

Currently, the most common ceramic slurry used in the production of shells for investment castings is comprised of alumina and silica. These refractory materials are typically mixed with an aqueous binder to form a viscous slurry. The aqueous binder is used to enhance the flow of the slurry and improve the inter-coat bonding. However, the aqueous binder eventually evaporates from the slurry and can leave gaps in the shell structure. This can cause defects in the final casting, such as a bloated or deformed surface.

This article discusses a new method of producing ceramic shells for investment castings that uses a geopolymer as a face-coat material. The geopolymer coating reduces the amount of alumina and silica needed, and it allows for an increase in both permeability and flexural strength. The result is a ceramic shell that has superior performance to traditional ceramic shells in both green and fired states.

The ceramic shells produced using this new technology have been successfully used in foundry practice. The resulting castings have their dimensions all within the required tolerance limitations. In addition, the geopolymer coating was found to significantly improve flexural strength of the ceramic shells, even after they were subjected to high temperatures. This result is significant because non-uniform thickness distribution of the shells is known to be the main factor responsible for shell cracking and bulging during casting.

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